I get those are the rules, but practically speaking I don't understand how that can work. I usually don't sell much, but say I sell $950 worth of stuff, a bunch of random items, say 50 in total. Most of this stuff I have had for years if not decades. How on earth am I supposed to know, let alone prove how much I paid for a strategy guide in 2003? If the initial cost can't be proven am I stuck paying tax on that entire $950?